Incorporating water-repellent pigments in viscose



Patented. Mar. 11, 1941 um'reo STATES mcoarom'rme warns-appraisalPIGMENTS IN vrscosn Hayden B. Kline, Cleveland, Ohio, asslgnor toIndustrlal Rayon Corporation, Cleveland, Ohio, acorporation of DelawareNo Drawing. Application July 13, 1937, Serial No. 153,379

1 Claim.

This application, which is a continuation in part of abandonedapplication Serial No. 4,693, filed February 2, 1935, for Manufacture ofcol- 5 of water-repellent pigments in viscose.

It has been customary in the manufacture-of viscose containing one ormore readily compatible pigments to incorporate the pigment or pigmentsat or soon after the time of the preparation of the viscose. Thus it hasbeen the-practice to mix in a dissolver cellulose xanthate, causticsoda, water, and the desired pigment or pigments. Sometimes all of thewater has been added with the caustic soda, the latter being in suchcase in the form of an aqueous solution;

but more often part of the water has been added with the caustic sodaand part with the pigment or pigments. In a great many cases thispractice of introducing one or more pigments com- 30- paratlvely earlyin the ageing schedule has tended to interfere with the ageing of theviscose, an operation which has been invariably carried out heretoforeat substantially the concentration employed in spinning. 2 To obviate'this difficulty, it has been proposed to prepare viscose of the usualspinning concentration; to filter, age, deaerate and otherwise treat theviscose in exactly the same manner as Viscose used in the manufacture ofunpigmented 30 products; and to introduce the pigment or pigments afterthe viscose is no longer in bull: but

' is actually in passage to the spinning machine.

An important objection to this process is that it is impossible toobtain uniform dissemination of the pigment or pigment-s, howeverreadily compatible with the viscose, in the few seconds that interveneprior to the time of spinning. Another important disadvantage is that ifthe pigment is to any extent water-repellent it is impossible to avoidthe necessity of dispersing the pigment in a large quantity of water thepresence of which, by modifying such important factors as theconcentration of the solution, make satisfactory spinning impossible.

The presentinvention, which relates to the incorporation in viscose ofwater-repellent pigments, departs from these and other known practicesin that it does not contemplate the initial preparation of viscose ofapproximately the concentration employed in spinning; rather, theinvention provides a process pursuant to which the viscose is made up ina concentration substantially higher than that desired for or useful inspinning. This is accomplished by withholding 55 a substantial part, say10%, of the water emored artificial silk, relates to the incorporation Im-ent or pigments. K 10 The invention thus involves temporarilywithholding a portion of the dissolvingwater, using it later, aftersubstantial completion of the agei'ng operation, to carry the pigment orpigments into the viscose at the required final concentra- 1-5 tion.This procedure is-based on discoveries as a result of which, by means ofa simple but highly significant departure from the usual routine, it

is possible to produce pigmented products of exactly the same physicalcharacteristics as unpigmented products; :1. e., pigmented products thephysical properties of which have not been adversely afiected as aresult of the use of unduly dilute viscose. The process maintainssubstantially unchanged the other characteristics of the pigmentedproduct, the manufacturing routine for the preparation of the viscose,and even the spinning operation itself. For practical reasonshereinafter pointed out, this is extremely important to the manufacturerof viscose products.

The making of viscose products involves the preparation at the outset ofthe viscose from which the products are to be fabricated. The first stepin the preparation of,viscose consists in steeping sheets of. aparticularly .pure form of cellulose, usually lugnTgrade-papenpulp, in asolution-0f caustic soda of carefully controlled concentration, for-aprecise time and at an exact temperature, all in order that thereactionbetween the cellulose and the caustic soda may proceed to apredetermined stage... Thereafter, a definite portion of the causticsoda solution is expressed and the sheets are takendmmediately to adisintegrating mill where they are broken (5 up into moist crumbs. Thesecrumbs are then stored in a temperature-conditioned room fora specifiedperiod of time.

At the close of the storage interval, the crumbs are churned with apredetermined amount of carbon disulphide to produce a compound calledcellulose xanthate."v This intermediate product is'dissolved, togetherwith a very carefully proportioned amount of caustic soda, in water, thedissolvingstep being conducted at a definite temperature for a preciseperiod of time. The resulting viscose is sent to a storage tank systemfor ageing for a definite period of time determined :by the character ofthe cellulose, the concentration of the original steeping solution, theamount of the caustic soda introduced in the dissolving step, the amountof carbon disulphide used, and the acidity of the coagulating bath. Theageing period is exceedingly critical, a variation of about one hour ona total ageing time of 72 hours being all that is permissible.

During the ageing operation, the viscose is filtered from tme to time toremove undesired reaction products.

After a final filtration, the viscose is sent to the spinning machines,from which it is pro- Jec'ted into a coagulating bath. All of the spinning machines must spin at the same time from the same batch of viscose,Wherefore the size of each batch of viscose must be such as to providefor all of the spinning machines for a definite time interval. To supplythem, successive fresh batches of cellulose must be started through thepreliminary steps at about one hour intervals. In order to supply asubstantial number of spinning machines, the size of each batch oi.viscose should be and ordinarily is in the neighborhood of 5000 pounds.

Each plant for the manufacture of viscose products has its ownparticular schedule 01' times, temperatures and concentrations for thepreparation of the viscose. To such empirically determined schedulesfound to produce satisfactory products manufacturers adhere with theutmost care, even minor departures from the schedule of temperatures,times and concentrations being scrupulously avoided. Seemingly minor andinsignificant departures from the schedule may profoundly alter theresults, to the extent, even, of rendering the product utterly useless.It is said that in the manufacture of viscose there are more than athousand critical variables between the preparation of the raw materialsand the completion of the product any one of which, if altered, mayresult in process failure.

One of these variables is the concentration of the viscose, whichthroughout the entire process of preparation of the viscose has alwaysheretofore been carefully maintained at a value within a fraction of oneper cent of the desired spinning concentration. As herelnabove noted, ithas been customary to make up the viscose in the first instance inapproximately the concentration desired for spinning, thereafterfiltering, ageing and deaerating it. The reason for performing thesevarious steps at substantially the spinning concentration is found inthe fact that efforts to spin at concentrations differing by more than afraction of one per cent from the proper spinning concentration havegiven rise to frequent process failures. If, for example, the departurefrom the proper spinning concentration is substantial, the viscosecannot even be spun.

The present invention involves the surprising 1 discovery that there isat least one respect in which the usual manufacturing procedure affordsa valuable margin of relative stability; namely, that while all of theother factors must be held carefully at their predetermined values, thesolution made by dissolving cellulose xanthate in the presence ofcaustic soda maybe made up with considerably less water than thatnecessary in the spinning solution without injury to or interferencewith the ageing process. Up to about 10% of the water may, withoutdisturbing the ageing schedule, be omitted and added at the close of theageing schedule to produce a spinning solution of the proper character,a range of permissible variation that is probably unique in the process.Most, if not all, of the other items must be maintained with an accuracyof better than about 1%, else the spinning solution is rendered useless.

The present invention thus modifies this highly sensitive procedure at apoint at which the unstable character of the viscose has been discoveredto be somewhat less pronounced.

It has been thought heretofore that the relationship between thecellulose content of the viscose, the amount of caustic soda, the amountof water, the ageing time, and the concentration of the coagulating bathare strictly interdependent. Such is certainly the fact as regards theamount of caustic soda, but the present invention depends in part uponthe discovery that, provided the over-all amount of caustic soda ismeanwhile maintained, a considerable amount of the water in which thecaustic sod-a and cellulose xanthate are dissolved may be temporarilywithheld. If it is later added at or toward the close of the ageingschedule, a normal viscose of proper concentration for spinning isnevertheless obtained.

That is, even though the amount of water in the viscose is vitallyimportant to satisfactory spinning, it is not necessary, contrary toprevious opinions, that all of the water be present in the viscosethroughout the ageing procedure.

In practicing the invention, the ordinary steeping, disintegrating,crumb storing and xanthating operations are conducted according to theempirically determined plant schedule, after which the'cellulosexanthate is dissolved in the presence of the usual amount of causticsoda in considerably less than the usual amount of water, as much as 10%of the water necessary to make up viscose of proper concentration forspinning being thus withheld. The resulting solution may be utilized forthe spinning of a plurality of different products by reducing theinitial :batch into division batches, each of which, prior to itsdelivery tothe spinning machines, is brought up to proper strength bythe addition of its proportionate part of the amount of water sowithheld. As already indicated, the step of making up the withheld watermay be advantageously employed to carry one or more water-repellentpigments into the viscose.

The addition of the readily compatible pigments ordinarily used fordelustering involves at the most the incorporation of but a few poundsof water without any perceptible dilution of the viscose; but theaddition of one or more waterrepellent pigments, such, for example, ascarbon black, is an entirely different matter. Carbon To color a typicalfive thousand pound batch of viscose with carbon black in a quantitysufficient to produce a satisfactory black product requires that aboutpounds of carbon black be added to the batch. This amount of carbonblack cannot be added dry even to a very large iii hatch, since it isnot wetted .by the viscose, nor can it satisfactorily be made up inwater to a paste of small volume. The carbon black must first be mixedwith something less than 500 pounds of water, roughly 60 gallons oiwater,

to maintain the particle size in the viscose. It added to ordinaryviscose in the manner heretoiore employed, this amount of water,approxiand water in quantities sufficient to bring the celluloseconcentration to 7.5%. This mixture is then filtered, aged in the usualway, deaerated and otherwise treated quite as would be viscose oi t.6%concentration. Shortly before the viscose is ready for spinning butwhile the viscose is still in bulk, the desired water-repellent pigmentis produced. If, for example, it is desired to manufacture a productcolored black by means of carbon black, there is introduced into theviscose an aqueous suspension of carbon black containing the exactamount oi. water suflicient to reduce the cellulose concentration of theviscose to the desired 6.6%.

Thus the invention comprehends, in its preferred form, the several stepsof preparing a batch of viscose 01' a relatively high concentration;treating it after the manner oi viscose of the ordinary kind to prepareit for spinning;

introducing the desired water-repellent pigment,

simultaneously diluting the batch in conjunction with the addition ofthe pigment to the proper spinning concentration: and spinning theviscose. The step of withholding part of the water employed in thepreparation of the viscose in order to use it in dispersing awater-repellent pigment to be later introduced is highly ad vantageougin'avoiding undue reduction of the cellulose concentration of theviscose.

I'his and other meritorious ieatures characterize the invention, whichis to be understood to be exemplified by rather than limited to theillustrative example above given.

Inasmuch as the pigment, even though waterrepellent, is introduced whilethe viscose is still in bulk, it is obviously possible to obtain a moresatisfactory dissemination of the pigment in the viscose than can beaccomplished by other methods. The introduction into a given batch ofthe amount of water previously withheld is conveniently used tofacilitate the step of mixin the pigment with the viscose,;moreespecially in that it permits bringing the pigment into the form of asuspension prior to its introduction into the viscose. Withholding thewater in the manner herein described has the advantage that it permitsoi the employment of a minimum of the apparatus, whichis an importantadvantage in view of the fact that filtering, ageing. deaerating andother steps require the employment for relatively long periods of timeof large numbers of filter presses, tanks and other items of equip ment.

It is possible to apply the invention to advantage in various otherprocesses than the viscose process. Thus, while the invention ispreferably employed in the manufacture of viscose products, in which, asstated, water is withheld in order to maintain the cellulose content ,ata substantially higher concentration than normally would be the case, itis also possible to employ the invention in the cellulose acetateprocess, withholding part of the acetone or other liquid employed as thesolvent. The nitrocellulose and cuprammonium processes may likewise beused, these processes heing modified as necessary to permit of thebelated introduction of part of the solvent or other liquid vehicle withthe pigment or pigments.

It is evident that numerous other modifications and changes may be madein the procedure described in the present application without in any waydeparting from the spirit oi the invention. It will be understoodthat-the term "carbon black as hereinbeiore and hereinafter used is notemployed in its strictest sense. but is intended to comprehend thediflerent types of carbon pigments which are commercially available.

it will further be understood-that as herein employed the term"liquid-repellent is not to be understood as limited to water, but asequally applicable to other liquids; e. g.. the acetone or other solventemployed in the cellulose acetate A process.

It is intended that the patent shall cover, by

suitable expression in the appended claim, whatever features ofpatentable novelty reside in the invention.

What is claimed is: i

The process of effecting the incorporation of a relatively largequantity of carbon black in viscose for the purpose of imparting a fullblack color to an extrusion product formed therefrom which processcomprises the steps oi! preparing a concentrated aqueous solution ofsodium cellulose xanthate of a consistency so high as to beimpracticable for satisfactory spinning even after prolonged ageing;ageing the solution according to the customary ageing schedule withoutin the meanwhile diluting the solution, as by the addition of water, toa concentration approaching that at which the solution is ultimately tobe employed; and, toward the end of the ageing schedule, introducing thedesired large quantity of .carbon black in the form of a physicalsuspension thereof in a quantity of water sumcient to reduce theconsistency of the solution for the first time from an impracticablyhigh concentration to a concentration prac-.

